1. Field of the Invention
The present invention relates to a chemical sensor which consists of a solid substrate and discrete layers which are applied thereon and have different compositions, said sensor being suitable for detecting ions or organic molecules.
2. Description of the Related Art
Sensors based on fluorescent dyes have long been known. For example, M. Azzawa et al. (Thin Solid Films 160 (1988), 477) describe a sensor in which one or more layers of a fluorescent dye are brought into contact with the analyte to be investigated. As a result of interaction with one or more components of the analyte, a change occurs in the intensity of fluorescence. As a rule, fluorescent substances which exhibit a reduction in fluorescence, i.e. quenching, are used. A similar application in the area of biosensors is described by M. Azzawa et al. in Thin Solid Films 180 (1989), 227.
Sensors which are based on fluorescence transfer and in which the fluorescence of dye 1 is transferred to a second fluorescent dye are also known. These systems use a second fluorescent dye which, for example, may be bound to a component of the analyte (cf. for example European Patent 150 905). The detection of energy transfer in waveguide structures by means of evanescent waves has also been described (Nature 320 (1986), 179).
O. S. Wolfbeis et al. have described a number of sensors which utilize the quenching of fluorescence due to potential-sensitive dyes, the Langmuir-Blodgett method being used in some cases (Analyst 113 (1988), 693; Anal. Chim. Acta 217 (1989), 1).
J. N. Roe et al. (Analyst 115 (1990), 353) describe a fiber-optical sensor in which the fluorophore and the ionophore valinomycin, which is sensitive to potassium ions, were applied in an inhomogeneous polymer layer about 6 .mu.m thick to the fibers.
The sensors described to date are either all based on direct quenching of the fluorescence by the analyte, are present together with an absorber in a polymer matrix or utilize potential-sensitive dyes.
The response times of such sensors are limited by the diffusion of the analyte in the sensor system, and a reference electrode which is intended to increase the selectivity is generally used. In many cases, dip coat layers which are relatively thick are used for this purpose.